In the production of gears and related toothed articles, one type of cutting blade commonly utilized is a blade known as a stick-type cutting blade made from a length of bar stock material such as M2 high speed steel. A plurality of such blades are secured in a cutter head mounted on a cutter axis of a gear cutting machine and are advanced into contact with a gear blank to form tooth profiles into the blank. Gear cutting machines utilizing such cutting blades are known in the art, as shown, for example, in U.S. Pat. No. 4,981,402 to Krenzer et al.
One form of a stick-type cutting blade is designed so that only the top surface and side surfaces (pressure side and clearance side) require grinding in order to sharpen the cutting blade while preserving the front surface of the blades. These cutting blades are known as "profile-sharpened" cutting blades. Profile-sharpened cutting blades are such that the length of each blade is reduced by each sharpening and for this reason the blades are provided with a front cutting surface length whereby the blades may be axially advanced in a cutter head slot as needed in order to provide adequate stock for restoring the surface profiles. Examples of such cutting blades can be seen in U.S. Pat. No. 4,260,299 to Ryan et al., U.S. Pat. No. 4,621,954 to Kitchen et al., and U.S. Pat. No. 4,575,285 to Blakesley.
Cutting blades such as those illustrated in the above-referenced patents comprise two sections, a base portion and a cutting end portion. The base portion is generally of a rectangular cross-section. The cutting end portion, however, includes a rake face extending nearly side-to-side across the front of the blade and oriented at a particular rake angle to produce relief away from the cutting edge. Due to this configuration, a blade may be utilized, for example, for cutting inside (convex) gear tooth flanks with a right-handed cutter (counter-clockwise cutter rotation) or for cutting outside (concave) gear tooth flanks with a left-handed cutter (clockwise cutter rotation). However, for cutting outside gear tooth flanks with a right-handed cutter or inside gear tooth flanks with a left-handed cutter, a "mirror-image" cutting blade is necessary, such a blade having a cutting edge on the opposite side of its front face and having a rake face extending in an opposite manner across the front face when compared to the cutting blade described above.
When the cutting blade is initially mounted in the slot of a cutter head, both the base portion and the cutting end portion are positioned in the slot of the cutter head with only enough of the cutting end portion extending beyond the cutter head surface as is needed to machine the desired workpiece. Excess blade length beyond the cutter head surface contributes to cutter instability. Even after the cutting blade is sharpened and it becomes necessary to axially reposition the blade in the slot due to its reduced length from the sharpening process, a part of the cutting end portion remains in the slot. Although the base portion of the cutting blade is fully supported in the cutter head, the cutting end portion which is located in the cutter head slot is not completely supported because of the portion of the blade body removed by the formation of the rake face of the cutting blade.
When axial advance of the blade in the slot reaches a point where only the base portion of the blade remains in the slot, that is, when axial advancement results in that part of the base portion adjacent the rake surface becoming essentially flush with the surface of the cutter head, the cutting blade will then be fully supported. However, this point in the axial advancement of the blade signifies the end of the useful length of the cutting blade since there is usually an inadequate amount of rake surface remaining on the front surface of the blade to permit another sharpening of the blade.
Consequently, during cutting of a workpiece, while the base portion allows for support at all four corners due to its rectangular cross-section, that portion of the cutting blade which is not supported at all four corners (the cutting end portion) in the cutter head slot, while being stable in many cutting applications, has a tendency to twist under conditions where the loads and stresses of cutting are high, such as when large amounts of stock material are removed by each pass of a cutting blade through the tooth slot of a workpiece. Twisting of the cutting blades effectively repositions the cutting edges of the blades and leads to unacceptable tooth flank surfaces being formed. Except for the final stage of the useful life of the cutting blade, the potential unstable condition due to the lack of complete support of the blade exists at all times during cutter operation.
In the above-cited U.S. Pat. No. 4,621,954, narrow portions on either side of the back surface of a cutting blade are included to provide clearance between a pair of cutting blades positioned in a single slot. However, the inclusion of these narrow portions on the back surface in no way influences the front face of the cutting end portion of the blade. There continues to be a lack of complete support of the portion of the blade removed by the formation of the rake surface.
Accordingly, it is an object of the present invention to provide a universal cutting blade blank having a front rake face and which is capable of being formed into a cutting blade regardless of tooth surface to be cut or direction of cutter rotation.
It is another object of the present invention to provide a cutting blade with mounting surfaces which will prevent twisting in the cutter head during cutting operations even though the cutting blade is provided a front rake face throughout its length.